In multi-carrier systems, as OFDMA (Orthogonal Frequency Division Multiple Access) transmission systems, the transmitted data is split into a number of parallel data streams, each one used to modulate a separate sub-carrier. In other words, the broadband radio channel is subdivided into a plurality of narrow-band frequency subcarriers, which are grouped into subchannels, each subcarrier being independently modulated with e.g. QPSK, 16 QAM, 64 QAM or higher modulation order allowing higher data rate per sub-carrier.
In such systems, the sub-carrier frequencies or subchannels can be allocated to a user channel on a short term basis (e.g. all 2 ms) as well as the modulation order per sub-carrier defining a transmission channel for each user should be updated on the same short term basis.
There are different ways to increase the overall throughput of the system.
Firstly, an efficient sub-carrier/modulation allocation should be performed to the different users, i.e when the best appropriate sub-carriers or subchannels are identified for a user, the optimal modulation to be used on these sub-carriers or subchannels should be appropriately selected. The higher modulation orders can only be used if the signal to noise and interference ratio (SINR) at the receiver is high enough to allow the demodulation.
Secondly, the network being a cellular wireless communication network, the frequency reuse should be appropriately chosen in order to reuse as many subchannels as possible in a cell without causing interference. For this purpose, the cell may be separated in sectors and subsectors and the set of available subchannels may itself be divided in a number of subchannel subsets, one predefined subchannel subset being used in one predefined subsector of the cell as shown on FIG. 1.
A cell centered on a base station BS is divided in 3 sectors A, B and C.
Each sector is further divided in 3 sub sectors A1, . . . , A3, B1, . . . , B3, C1, . . . , C3.
Assumed that N frequency subchannels are available in the network, 3 groups of subchannels may be constituted [0,n1], ]n1,n2], ]n2,N] and allocated in the following way to the sub sectors:
sub channel group [0, n1] is allocated to users in subsectors A1, B1, C1,
sub channel group ]n1,n2] is allocated to users in subsectors A2, B2, C2,
sub channel group ]n2, N] is allocated to users in subsectors A3, B3, C3.
This fixed allocation guarantees low inter sub-sectors interference since no situation occurs in which the same subchannel subgroup is used in two contiguous portions of the cell. This allocation scheme is a frequency reuse 1 scheme since all frequency sub channels are used simultaneously in all cells and even in all sectors of each cell. Once the frequency subgroup has been identified for a subsector, the users located in the corresponding subsector are allocated one or more of the frequency subchannels of the frequency subgroup for communicating with the base station.
It is an object of the present invention to further improve the capacity in a frequency reuse 1 wireless radio communication network.